The present invention relates to a power semiconductor component, in particular a unipolar power semiconductor component, with a drift zone and a compensation zone made of a high-dielectric (high-k) material extending along the drift zone.
The drift zone of a power semiconductor component, for example of a power MOSFET, serves in a known manner to take up an electric field when a blocking voltage is present. In this connection, the on resistance of the component and the with-stand voltage thereof are dependent on the dimensions of the drift zone and the dopant concentration present in the drift zone. In this case, it holds true—if no additional measures are implemented—that the on resistance is all the lower, the shorter the drift zone in a current flow direction and the higher the doping concentration thereof. Conversely, however, the withstand voltage of the component also decreases with shortening of the drift zone and an increase in the dopant concentration.
With a component driven in the off state, providing a compensation zone made of a high-dielectric material effects a compensation of part of the dopant charge present in the drift zone due to the doping. This compensation effect is caused by a strong polarization of the high-dielectric compensation zone, with the polarization charges hereby compensating for dopant charges in the drift zone. For a given blocking voltage, this compensation effect reduces the electric field strength in the drift zone in the current flow direction, so that, for the same dielectric strength, the doping concentration of the drift zone can be increased in comparison with conventional components in order thereby to reduce the on resistance.
For the realization of power components, suitable high-dielectric materials have the disadvantage that the dielectric constant is greatly dependent on the temperature. Referring to Hilton et al.: “Dielectric Properties of Ba1-xSrxTiO3 ceramics”, J. Phys. D: Appl. Phys. 29 (1996) 1321-1325, by way of example, the relative permittivity ∈r of Ba0.7Sr0.3TiO3 is ∈r=5000 at a temperature of T=300 K and decreases by a factor of 10 to ∈r=500 in the event of a rise in the temperature to T=450 K. For the application of said material as a compensation zone in a power semiconductor component this means that the compensation charge decreases by the factor of 10 in a manner corresponding to the relative permittivity in the event of a rise in temperature from 300 K to 450 K, which leads to a reduction of the dielectric strength of the component. Consequently, the dielectric strength of the component is greatly dependent on the temperature.
This great temperature dependence of the relative permittivity of high-dielectric materials is problematic in particular because power components have to be fully functional over a wide temperature range, for example from −55° C. (218 K) to 150° C. (423 K).